Black Box Testing

• What is Black Box Testing?
• Advantages of Black Box Testing
• Black Box Testing Process
• Types of Black Box Testing
• Black Box Testing Techniques

What is Black Box Testing?

Software testers testing an application software to verify if it works for end-users as intended, without being concerned about its inner workings represents black box testing.

• The software testers need not have prior knowledge on the internal code structure, implementation details of each functionalities and internal paths or flow of the software application to be tested.
• Black Box Testing focuses primarily on the outputs generated by the different functionalities of the software application to be tested based on the inputs submitted to them. This is entirely based on software requirements and specifications.

Advantages of Black Box Testing

Major advantages of are,

• Software Testers perform black box testing from an end-user’s perspective. So the software tester does not need to have technical knowledge or programming skills to implement it.
• Crowdsourced or outsourced testers can execute black box testing.
• After obtaining the software requirements and specifications, one can create test cases and test scenarios immediately.
• Both software testers and software developers work independently without interfering in each other’s space which reduces unwanted bias.
• Black Box testing helps in identifying ambiguity and contradictions in the functional specifications of the application/project.
• It is more effective for large and complex applications.
•  Black box testing is performed from a common user’s point of view. This gives it a higher possibility of satisfying customer expectations and needs.

Black Box Testing Process

We provide below a brief explanation of the commonly followed sequence of steps to carry out this type of testing.

1. Initially, the requirements and specifications of the application software to be tested are examined. Properly documented SRS (Software Requirement Specification) of the application/project should be available.
2. The software tester chooses valid inputs (positive test scenario) to use for the test cases that check whether the application under test processes them correctly. Additionally, we choose some invalid inputs (negative test scenario) to use for the test cases that verify whether the application is able to detect them.
3. The next step involves identifying the set of test scenarios for which we need to frame test cases.
4. Software tester constructs test cases with the chosen inputs for the identified test scenarios.
5. Software Tester determines expected outputs for the chosen inputs for each test case.
6. Software Tester executes the test cases.
7. Software tester compares the actual outputs with the expected outputs.
8. Failed test cases are marked as Defects/Bugs and addressed to the development team to get them Fixed.
9. Finally, the software tester retests the defects once they are rectified to confirm that they are not recurring.

Types of Black Box Testing

The 3 most prominent types are,
1. Functional Testing: – Black box testing can be used to test the functions or features of the application software under test. It covers the functional requirements and specifications of a software program.

• Functional testing is performed by providing a certain input to a function or a feature and verifying if the output from it meets the conditions specified in the software requirements and specifications.
• Various types of functional testing are Smoke Testing, Unit Testing, Integration Testing, User acceptance testing, etc., and can be performed either manually or by automation.

2. Non-Functional Testing: – Black box testing can also be used to test non-functional requirements of an application software such as performance, scalability, security and usability.

• Non-functional testing is important for maintaining and improving the quality of an application software as real end-users may experience critical issues while using the application that are not related to its functionality.
• Various types of non-functional testing include Load Testing, Performance Testing, Stress Testing, Usability Testing, Scalability Testing, etc.

3. Regression Testing: – Regression Testing is normally done after code corrections, upgrades or any other maintenance activities on the application software to confirm that the new code modifications haven’t adversely affected the existing functionalities or features of the application software.

“Any application software must go through regression testing to rule out the possibilities of unseen implications after its modification.”

Black Box Testing Techniques

The prominent test case design strategies commonly applied for Black Box Testing are as follows.

1. Boundary Value Analysis: –

• Used to identify the bugs that arise due to the lower and upper limits of data applied as inputs.
• We initially determine the boundaries for input values and then select values that are at the boundaries as test data. Additionally, we select values that are near the inside or outside of boundaries.
• Test the application software with test cases that have these extreme values of test data as inputs. This increases the efficiency of testing as the probability of finding errors increases at these boundaries.

2. Equivalence Partitioning :-

• We partition the test data inputs into groups based on their similarity in the outcome and use only one test data input from each group for testing to examine the results.
• This testing assumes that a test case will run identically for equivalent inputs from the same group. Therefore, we pick and test only one input value from each group.

3. Decision Table Testing :-

• A decision table has a different set of input conditions and their corresponding expected outcomes on each row.
• Software testers initially identify rules, which are a combination of conditions.
• We further identify the outcome of each rule in order to design a test case for each rule.
• This technique works well when multiple input combinations and possibilities are present.

4. State Transition Testing :-

• Software testers can design test cases that examine the transition of states if they identify a state transition action. An example- for a system that locks the account after five failed login attempts, a test case can check what happens at the sixth login attempt.
• This testing technique applies to those types of applications that provide a specific number of attempts to access a functionality.

5. Error Guessing :-

• Involves testing for common errors made by software developers while developing similar software applications.
• The software testers can make use of the experiences they have gained by testing similar applications to guess the error-prone areas.
• Software testers can identify high-risk code sections that they need to test thoroughly by knowing possible errors or error-prone areas.

6. Cause Effect Graph :-

• We initially identify the causes (input conditions) and effects (output conditions) in this testing technique, and then we produce a Cause-Effect Graph that depicts the link between the causes (inputs) and the effects (output). Based on this cause-effect graph, we generate test cases.
• This testing utilizes different combinations of inputs and outputs. The coverage of cause-effect graphs is based on the percentage of combinations of inputs tested out of the total possible combinations.

Conclusion

• By testing software from a user’s point of view, black box testing helps to mitigate the risk of software failures at the user’s end. If done correctly, it is an excellent way to ensure that the system works in line with end-users expectations without worrying about the system’s inner workings.
• Black box testing is the easiest and fastest solution to investigate the software functionalities without any coding knowledge.
• It helps in exposing discrepancies present in the software requirement specifications prepared prior to the development of the application software thus facilitating an excellent finish for the application.

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Rajesh K

Possessing Post Graduation in Applied Electronics with a specialization in Microprocessors and embedded systems, I started my career as a faculty in computer applications. Shifted to IT industry after few years and worked as a Quality Analyst for almost 7 years.